The conversion of coal into an essentially ash-free high melting carbonaceous material has received a great deal of investigation and developmental work. Demonstration plants have been designed and constructed for Gulf Oil Company's solvent refined coal process, HRI, Inc.'s H-Coal process and EXXON's donor solvent process. These processes produce a low ash, high melting, high sulfur, high nitrogen containing solid which is useful only as a boiler fuel. These processes are referred to as coal liquefaction.
Less work has been done on the liquefaction of lignite, however, although lignite represents one of the great energy resources of the United States. The principal investigation of the liquefaction of lignite was done at the University of North Dakota under the sponsorship of the U.S. Department of Energy on what was called "Project Lignite". The process design unit had a nominal designed capacity of fifty pounds of lignite feed per hour. It produced approximately fifteen pounds per hour of solvent refined lignite, a solid at room temperature. The solvent refined lignite process produced a high melting solid which is essentially ash-free but contains 0.98% sulfur and 1.07% nitrogen. This material is suitable only as low grade boiler fuel. Its high nitrogen content preclude its use as a substitute for crude oil in conventional petroleum refining. Nitrogen compounds quickly poison the catalysts used in petroleum processing. The presence of sulfur is less objectionable because effective processes for the desulfurization of feedstocks have been developed. In order then to convert solvent refined coals and lignites into feedstocks acceptable to a conventional petroleum refinery, it is essential that a method be found which will remove most of the nitrogen compounds from the solvent refined coals and lignites without changing them greatly otherwise. The purpose of this invention is to show how this can be done. Lignite has also been liquified by the EXXON donor solvent process and by the H-Coal process although in smaller quantities than that from bituminous coals.